@Char1997 here are a few facts for you:
www.equalityadvisoryservice.com/
Helpline 0808 800 0082
^ check out the EASS website, it has a good section with general info on pg as a protected characteristic.
Fact is, they cannot accuse you of dishonesty for not discussing your pregnancy if you are still >15 weeks from your due date. Shows how archaic their knowledge is as an employer. It should have no bearing on whether you are the right person for the job. They are living in the dark ages, and their attitude is decades behind the law.
EHRC research shows that six in ten employers think that a woman should have to disclose whether she is pregnant during the recruitment process. 50% of those interviewed believe it is reasonable to ask women if they have young children during the recruitment process.
In one sense you have made a lucky escape. Imagine working for this company, if they breach EqA legislation now, they are likely to be practicing discrimination against their employees.
Equality Advisory and Support Service is a free government-funded helpline, so give them a call for a chat, as they can give you specific guidance about your Claim and likelihood of success at Tribunal. As Tribunal is now fee-free, you have nothing to lose at this stage, and it could force the company to have to compensate you to avoid them incurring the cost and reputational damage of tribunal.